It is the usual practice to collect the sample in a long tubular container. The container is open at its bottom end and, when the container is driven into the ground soil, the sample enters the container. After withdrawal from the hole, the container may be cut or slit along its length in order to remove the sample. The tubular container is normally destroyed in the process of removing the sample.
The invention is concerned with a need to provide a sampler for use in extracting samples in reasonably soft ground, from depths below the surface, without the need for a drill, and in remote locations. Such a sampler should be light to carry, and should need minimum ancillary equipment. The sampler should have these facilities without compromising the quality of the samples.
These factors will now be considered in more detail:
1. Regarding the accessibility of the site from which the sample is to be taken, the invention is for use in those cases where it is not economical to carry and install heavy equipment, power supplies, drill rigs, etc. PA1 2. Regarding the depth from which the sample is to be taken, the invention is for use in those cases where it will be possible to reach the required depth using a few sections, and where it will be possible to drive the sampler to the required depth by the use of a hammer. There is a limit to the depth to which it is economical to drive a sampler by hammering from the surface, so that for deeper samples, it would be necessary to use a drill. The invention has no particular benefits in the case where the sample is being taken right at the surface, ie where the sampler does not have to travel down through a layer of overburden to reach the sampling interval: there are many inexpensive ways of taking samples from the surface. PA1 3. Regarding the type of groundsoil likely to be encountered, both in the sample, and in the ground above the sample, through which the container will have to pass, the invention is for use in those cases where the cohesiveness, abrasiveness, penetration-resistance, and water-content of the soil are such that the container can be simply driven into the ground, without drilling. Even when the groundsoil is soft, the invention would not be used if the groundsoil were to contain large cobbles. PA1 4. Regarding the pattern of sampling required, the invention is for use in those cases where ease of movement of the sampling apparatus to a different site is required, such as when taking samples at regular points on an area grid, for example. PA1 5. Regarding the depth accuracy required for the sample, the invention is for use in those cases where an accurate knowledge is required of the depth from which the sample came. The invention is also for use in those cases where it is required to take samples from different depths, using the same hole.
In some techniques for recovering samples, the procedure includes flushing water down the hole. This may spoil the sample, especially if it is the groundwater characteristics of the sample that are being studied. The invention is for use in cases when it is desired to avoid adding water to the hole.
One of the problems encountered when recovering samples of very soft, almost-cohesionless, groundsoil is that the sample tends to fall out of the containing tube as the tube is being withdrawn out of the hole. The invention provides a good resistance to the sample falling out of the container.
A particular advantage of the invention is that all the equipment needed to recover samples can be carried on a light truck of the rough-terrain type. A two man crew is normally all that is needed for operating the equipment used in the invention.
The invention is particularly addressed to the taking of samples in soft ground at reasonably shallow depths in remote areas. The invention is particularly concerned with how such samples may be recovered in an economical manner, without compromising the integrity and reliability of the sample.
In the type of sample-taking operation with which the invention is concerned, the operation is carried out in two distinct stages. First, the sampler is driven down through the ground to the level at which sampling is to start, and nothing enters the container during this stage. Then in the second stage, the sampler is driven further into the ground, and now the sample does enter the container.
The main problem faced by the designer of equipment for taking samples from soft ground is that the force required to drive the container down into the ground, even through soft soil, is enough to collapse the sample containing tube. The problem can of course be solved by using a more robust container, but then the container would be expensive. Also, if the container were more robust, it would be hard to cut open the container, for removing the sample. From the standpoint of economy, and of ease of exposing the sample, the container tube should be thin: but from the standpoint of drivability, the container should be robust.